Automatic choke mechanism



July 5, 1966 P. E. BRAUN r-:TAL

AUTOMATIC CHOKE MEGHANISM 5 Sheets-Sheet l Filed June 20, 1965 INVEN'TR`BY M z2. im CSV/mm2! d.. uZZA,

July 5, 1966 P. E. BRAUN ETAL AUTOMATIC CHOKE MECHANISM 5 Sheets-Sheet 2Filed June 20, 1965 PAU/ f, @Rau/V @E i ,4455er ,4. FWaC/wvo INVENTOR5July 5 1966 P. E. BRAUN ETAL AUTOMATIC CHOKE MEGHANISM 5 Sheets-Sheet 5Filed June 20, 1963 PAK/L E. SAD/40N /Mfkr A. PRacH/VO INVENTOR5 UnitedStates Patent Gti-ice 3,259,377 Patented July 5, 1966 3,259,377AUTOMATIC CHUKE MECHANISM Paul E. Braun, Birmingham, and Albert A.Pruchno, Detroit, Mich., assignors to Ford Motor Company, Dearborn,Mich., a corporation of Delaware Filed June 20, 1963, Ser. No. 289,201 1Claim. (Cl. 261-39) This invention relates' to an automatic chokemechanism for the charge forming device of an internal combustion engineand more particularly to an .automatic choke mechanism having animproved suction motor for modulating the position of the choke valve inresponse to engine intake manifold vacuum.

The conventional automatic choke mechanism employs a thermallyresponsive device, `generally a thermostatic spring, to position lthechoke valve in response Ito temperature variations. During lowtemperature cranking, the choke valve should be fully .closed to .permiteno-ugh fue-l for combustion to be drawn into the cylinders of theengine. The choke valve should pantially open once the engine commencesto run to allow ysuiiicient air linduction for sustained operation.

Engine intake manifold vacuum offers a convenient signal of the airrequirements of the engine. It has been common practice, therefore, toemploy intake manifold vacuum as `a source of power for opening Athechoke valve once the engine has started. This has been accomplished.through the use of an unbalanced choke valve, lthat is opened inresponse to the pressure `differential on opposite sides of the chokevalve, or by the use of a separate suction motor, that acts upon thechoke valve thro-ugh an actuating linkage. It has also been Icommon-practice to combine the use of an unbalanced choke valve and a separatesuction motor in a single choke mechanism.

Automatic choke mechanisms employing separate suction motors .havealmost universally resorted to piston type motors. The piston motor isexpensive to fabricate land also adds cost to the choke mechanism sincea link age system is required Ito translate the reciprocatory motion ofthe piston into rotary movement of the choke valve.

It is, therefore, the principal object lof this invention to provide animproved suction motor lfor an automatic ch-oke mechanism of an internalcombustion engine charge forming device.

The thermally responsive element of an automatic choke mechanism isessentially a linear device. That is, the degree of temperature inducedchoke valve movement bears `a direct relation to the change -intemperature of the thermally responsive element. The choke requirementsof la warming engine do not bear a directre-lat-ion to the increase intemperature of the thermally responsive element since the engine cant-olerate a progressively decreasing amount of choking as itstemperature increases. A conventional choke mechanism, therefore,provides a greater amount of choking alt intermediate enginetemperatures than 4is required and decreased fuel economy results.

It is a Ifurther object of this invention to provide an improvedautomatic choke mechanism that accelerates the opening of the chokevalve during engine warm up.

An automatic choke mechanism comprising .this invention includes a chokevalve that is imovably supported in an induction passage of a .chargeforming device. A thermally responsive element is operatively connectedto the choke valve for moving the choke valve between an opened and aclosed position in response to temperature variations. A suction motoris provided for modulating the position of the choke valve in responseto variations in engine intake manifold vacuum. The suction motorcomprises a cavity deiined -at one side by a movable wall. The cavity isvented to the intake manifold so lthat the wall will be moved inresponse to manifold pressure variations. After the wall moves `apredetermined amount, a substantially increased amount -of leakage ispermitted trom the cavity to retard tfurther movement of the wall. Theair transfer, because of the leakage, -is employed to draw heated airacross the thermally responsive element.

In one embodiment of the invention, the heating of the thermallyresponsive element -is accelerated as the choke valve opens lbypermitting an increasing Iflow of air through the cavity.

In a second embodiment of the invention, the leakage is decrease-d afteran initial increase to permit a strengthened torce by the suction motorto accelerate the rate of opening of the choke valve.

The novel suction moto-r incorporated in this choke mechanism comprisesa housing having a cavity in which a vane oscillates -to function as themovable wall. The vane is connected bythe choke linkage to the chokevalve to modulate the position of the choke valve in response tovariations in intake manifold vacuum.

Further objects and advantages of this invention will be more apparentas -this description proceeds, particularly when considered inconjunction with the accompanying drawings, fwherein:

FIGUR-E `1 is 4a partially exploded view oi a portion of an internalcombustion engine charge forming device embodying this invention. 4

FIGURE i2 is a cross sectional view -of ra portion of the chokeactuating mechanism shown in FIGURE 1 and is taken along line 22 ofFIGURE 3.

FIGURE 3 is a cross sectional view taken generally along the line 3 3 ofFIGURE 2.

FIGURE 4 is a cross sectional view taken generally along line 4-4 ofFIGURE 2.

FIGURES 5-7 are schematic views of the automatic choke mechanism showingvarious stages during the operation.

FIGURE 5 illustrates the position of the mechanism during the crankingof a cold engine.

FIGURE 6 shows the position of the mechanism immediately after the coldengine has started.

FIGURE 7 shows the position of the mechanism when the engine ispartially warmed.

FIGURE 8 is a cross sectional view taken along line 8 8 of FIGURE 5.

FIGURE 9 is a cross sectional view in part similar to FIGURE 8 showinganother embodiment of the invention.

Referring now in detail to the drawings, a charge forming device for aninternal combustion engine is indicated generally at 11. A choke valve12 is rotatably supported by a choke valve shaft 13 in an inductionpassage 14 of the charge forming device 11. The choke valve 12 isrotatably positioned in response to variations in engine temperature andintake manifold vacuum by the automatic choke actuating mechanismindicated generally at 15.

The automatic choke mechanism 15 includes a choke housing 16 havingthree inwardly extending bosses 17. Bolts 18, which extend throughapertures 19 formed in the bosses 17, are threaded into the body of thecharge forming device 11 to secure the choke housing 16 to the chargeforming device. An insulating cover 21 is affixed to the housing 16 by asheet metal clamp 22 and screws 23 which pass the apertures in the clamp22 and are secured in threaded apertures 24 formed around the peripheryof the housing 16. The interior of the cover 21 is thermally insulatedfrom the choke housing 1d by .a steel disc 25 and a composition disc 26interposed between the cover 21 and the housing 16.

A thermally responsive spring 27 contained within the cover 21 has itsinner end 28 affixed to a slotted inwardly extending projection 29formed at the center of the cover 21. The outer end of the thermallyresponsive spring 27 is coiled as at 31 for the reception of anoutwardly extending portion 32 of a lever arm 33. The steel andcomposition discs and 26 are slotted, as at 34 and 35 respectively, toprovide clearance for the rotary movement of the lever portion 32. Thehousing 16 is also provided with a rst cavity 36 in which the lever arm33 oscillates.

The lever arm 3 is connected by an integral hub portion 37 to a chokeactuating shaft 38. The choke actuat ing shaft 3S is journaled in thehousing 16 by a bushing 39 and extends inwardly toward the chargeforming device 11. A level 41 is affixed to the inner end of the chokeactuating shaft 38 by a nut 42. A link 43 has a lower outturned end 44that extends through an aperture 45 in a lever 1. A Cotter key 46 holdsthe end 44 in engagement with the lever 41 whereby movement of the lever41 will be transmitted into movement of the link 43. An inwardlyextending end 47 of the link 43 extends through an aperture 48 formed ina llever 49 that is aiiixed to the choke valve shaft 13. A snap ring(not shown) holds the link end 47 within the lever 49. The thermallyresponsive spring 27 acting through the levers 33 and 41, link 43 andlever 49 position the choke valve 12 in response to temperaturevariations.

A suction motor, indicated generally at 51, is provided to modulate theposition of the choke valve 12 in response to variations in enegineintake manifold vacuum. The suction motor 51 comprises a second cavity52 formed in the choke housing 16. A vane 53 is supported foroscillation within the second cavity 52. The vane 53 conveniently may beformed integral with the hub 37 and lever arm 33 as a molded one-pieceplastic element. The vane 53 acts as a movable wall within the secondcavity 52 to define an expansible chamber. The second cavity 52 isexposed to engine intake manifold vacuum on one side of the vane 53 by apassage 54 that extends from the second cavity 52 through one of thebosses 17 of the housing 16 into the charge forming device 11 at a pointin the induction passage 14 below the throttle valve (not shown).

Operation When the engine is cold, the thermally responsive spring 27will contract and rotate the lever arm 33 in a counterclockwisedirection. The choke actuating shaft 3S and lever 41 are also rotated ina counterclockwise direction to draw the link 43 downward. Downwardmovement of the link 43 is transmitted into counterclockwise rotation ofthe lever 49 and choke valve shaft 13 to bring the choke valve 12 to afully closed position (FIGURE 5 During cranking, insufiicient intakemanifold vacuum is generated to cause any action of the suction motor51. As soon as the engine lires and commences -to run, however, therewill be a sudden increase in intake manifold vacuum. The intake manifoldvacuum is exerted through the passage 54 into the second cavity 52 onone side of the vane 53. The decrease in pressure on the one side ofvane 53 causes the atmospheric pressure acting on the opposite side ofthe vane 53 to rotate the vane in a clockwise direction. The clockwiserotation of the vane 53 is transmitted to the choke actuating shaft 38and lever 41. The rotation causes the link 43 to move upwardly androtate the lever 49 and choke valve shaft 13 in a clockwise direction topartially open the choke valve 12 (FIGURE 6). The opening of the chokevalve 12 permits suiicent air flow through the induction passage 14 forsmooth engine operation.

The degree of opening of the choke valve 12 is controlled by forming theinner wall of the second cavity 52 in the manner shown in FIGURE 8. Theinner wall of the second cavity 52 is formed with a first surface 55that is closely spaced from the adjacent surface of the vane 53. Theclosely spaced surfaces permit only very limited air leakage past thevane 53 and substantially the full force Cil of the intake manifoldvacuum is exerted upon the vane 53. At a point corresponding to thedesired degree of initial choke valve opening, the surface 53 ends and asharply increased clearance between the vane 53 and a choke housing 16is provided by the stepped wall surface 56. When the vane moves to theposition shown at 53a (corresponding to FIGURE 6), a substantiallyincreased rate of air leakage past the vane 53 is permitted. This causesa sudden decrease in the vacuum force acting upon the vane 53 andfurther opening of the choke valve 12 is retarded.

The air leakage past the vane 53 is employed to draw heated air .acrossthe thermally responsive spring 27 in a manner now to be described. Atubular .projection 57 extends upwardly from Athe surface 55 of thechoke housing 16 through apertures in the insulating discs 25 and 26into the interior of the cover 21. Projection 57 is vented at 58 to theinterior of the cover 21. The projection 57 is internally bored as at 59and communicates with an air inlet 61 by means of a passage 62 formed inthe choke housing 16 (FIGURE 2). A conduit extends from the air inlet 61to exhaust manifold heat stove (not shown).

The air leakage across the vane 53 causes a pressure drop on the side ofthe vane 53 away from the second cavity 52, This decreased pressure istransmitted through the slots 34 .and 35 in the discs 25 and 26 to theinterior of the choke housing cover 21. Decreased pressure in the cover21 causes heated air `at atmospheric pressure to be drawn across theexhaust manifold stove. The heated air enters the cover 21 through theair inlet 61 `and vent 58. After circulation around the thermallyresponsive spring 27, the yair passes through the 'apertures 34 'and 35into the second cavity 5.2 past the vane 53. The heated air isdischarged into the intake manifold through the passage 54.

As has been earlier noted, it is desired to have the choke valve 12 openmore rapidly as engine temperature increases. To accomplish this result,the wall surface 56 of the cavity 52 is formed with an increasingclearance between the vane 53 as the vane 53 rotates in a choke valveopening direction. The increased clearance causes increasing amounts ofheated air tto be drawn into the choke cover 21. The thermallyresponsive element 27 is heated more rapidly, therefore, and anaccelerated rate of choke valve opening is accomplished.

As the thermally responsive spring 27 becomes further heated, the chokeactuating shaft 38 :and lever 41 `are rotated in a clockwise direction.Clockwise rotation raises the link 43 and rotates the lever 49 and chokevalve shaft 13 in a clockwise direction to open the choke valve 12(FIGURE 7). The position of the vane 53 relative to the wall surface 56of the cavity 52 during warm engine operation is shown at 53h in FIGURE8.

The -accelerated choke valve opening may also be laccomplished byforming the inner wall of the second cavity 52 in a manner shown inFIGURE 9. In this embodiment the first surface 55 of the inner wall isalso closely spaced from the vane 53 so that minimum air leakage willoccur past the vane during initial movement. A stepped surface 71 isprovided which permits an increased amount of air ow after the desiredinitial degree of choke valve movement. Due t-o the substantiallyincreased clearance, a substantially increased rate of -air flow willoccur past the vane 53 to retard further opening of the choke valve 12.The surface 71 is then provided with la decreasing amount of clearanceas the vane 53 moves t-oward the choke opened position. Because of thedecreasing clearance, an increasing amount of Vacuum force will beexerted upon the vane 53 to accelerate the opening of the choke valve12. In this embodiment the lamount of heated air will decrease to `someextent as the choke valve opens.

It is to be understood that the invention is not to be limited to theembodiments shown and described, but that further changes andmodifications may be made without departing from the spirit and scope ofthe invention as defined bythe appended claim.

We claim:

An automatic choke mechanism for the charge forming device of aninternal combustion engine comprising a choke valve movably supported in-an induction passage of the charge forming device, a thermallyresponsive element, a suction motor for modulating the position of saidchoke valve in response to changes in intake manifold Vacuum, saidsuction motor comprising a housing having an `annular cavity formedtherein and means mounting -a radially extending vane for rotation insaid cavity, at lea-st one wall of said cavity being recessed adjacentsaid vane to provide a varying clearance with said vane, a lever armintegrally formed with said vane, means affixing said thermallyresponsive element to said lever arm for exerting -a force on said leverarm in response to tem- References Cited by the Examiner UNITED STATESPATENTS 2,060,538 11/1936 Speed 261--39 2,325,372 7/1943 Coffey 261--392,969,964 1/196'1 Highley 261-39 3,058,727 10/*1962 Lucas 261-39 i HARRYB. THORNTON, Primary Examiner.

T. R. MILES, Assistant Examiner.

